Shifting point 07 with auto

This is my second summer with the truck and I have noticed that the truck shifts very late when I have the air on. It won't go into 5th until 40 mph unless I ease up on the pedal and reapply pressure ever so lightly. Now, if I hit the air conditioner button it goes into 5th as soon as I touch it. I can't say for sure if it did it last summer since I drove highway to work. This year I go back roads to save some miles. I have 41,000 miles so it's out of warranty. I'm thinking it is a computer problem but I am wondering if anyone has had the same problem. BTW, all the shifts come later when the air is on but the last one is most notable since it seems so unnatural for the engine to be turning the rpms it is for the speed I am going.